But the man in office about half a year still likes Japan and Japan likes him.
The relationship is especially crucial for Japan, a U.S. ally that has given Southeast Asia aid and investment for decades to out-run China.
China distrusts Japan.
Unlike China, however, Japan doesn't normally try to control the resources or political trends in countries where it sends money.
Japan also pledged military aid to Vietnam, which is no friend of China, in 2015.